Throughout this disclosure, various patent and technical publications are identified by an identifying citation or an Arabic numeral, the full citations for which are found immediately preceding the claims. These citations and the publications referenced within the present specification are incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Innate immunity is the first line of host defense. In response to invading pathogens, pattern recognition receptors (PRRs) sense pathogen-associated molecular patterns (PAMPs) that are structural components or replication intermediates (Medzhitov, 2007; Takeuchi and Akira, 2010; Ting et al., 2010). PRRs include the cytosolic receptors (e.g., cGAS, IFI16, RIG-I-like and NOD-like receptors) and the membrane-anchored Toll-like receptors (TLRs) and C-type lectins. Upon binding to PAMPs, PRRs recruit cognate adaptor molecules that signal to activate two closely-related kinase complexes, IKKα/β and TBK-1/IKKε. IKKα/β phosphorylates and induces the degradation of the inhibitor of NF-κB (IκBs), leading to the nuclear translocation of NF-κB (Chen et al., 1996; Zandi et al., 1997). TBK-1/IKKε can directly phosphorylate interferon regulatory factors (IRFs) to induce its dimerization and translocation into the nucleus (Fitzgerald et al., 2003; Sharma et al., 2003). Along with other transcription factors, nuclear NF-κB and IRFs coordinate to up-regulate the expression of many immune genes to engender an antiviral state (Bhatt and Ghosh, 2014). The cytosolic RIG-I receptor is a genuine RNA sensor that, in response to viral infection, activates NF-κB and IRFs through the mitochondrion antiviral signaling (MAVS) protein (Kawai et al., 2005; Meylan et al., 2005; Seth et al., 2005; Xu et al., 2005). Studies entailing gene knockout mice demonstrate that loss of RIG-I or MAVS severely impairs host innate immune response and greatly increases viral replication (Kato et al., 2006; Sun et al., 2006). Not surprisingly, viruses have evolved diverse strategies to halt or hijack antiviral signaling downstream of RIG-I and MAVS (Chan and Gack, 2015; Feng et al., 2013).
Post-translational modification (PTM) is a major means to regulate protein function and underpins diverse fundamental biological processes. First reported more than five decades ago (Mycek and Waelsch, 1960), deamidation of asparagine/glutamine in protein has long been regarded as a non-specific process associated with protein “aging”. Early protein deamidation research surveyed the overall deamidation of the cellular proteome, and led to the postulate that non-enzymatic protein deamidation serves as a biological clock for protein “aging” (Robinson and Robinson, 2001; Weintraub and Deverman, 2007). As such, research in protein deamidation is scarce and accordingly Applicant's understanding is rudimentary at best. A few proteins (e.g., Bcl-xL and 4EBP2) were shown to be regulated by deamidation in mammalian cells, which was postulated to be the consequence of an increase in cellular pH (Bidinosti et al., 2010; Deverman et al., 2002; Dho et al., 2013). Recent studies demonstrate that pathogenic bacteria secrete effectors to deamidate key signaling molecules to evade host immune defenses (Cui et al., 2010; Sanada et al., 2012) and manipulate cellular signaling (Flatau et al., 1997; Schmidt et al., 1997), indicating that protein deamidation can be catalyzed by bacterial enzymes and is highly regulated. The roles of protein deamidation in metazoan remain largely unclear.